1. Field of the Invention
The present invention generally relates to microwave amplifiers and, more particularly, to a low noise parametric amplifier of modular construction which achieves a high degree of reliability without resort to parallel redundancy.
2. Description of the Prior Art
Communication satellite earth terminals have evolved from the experimental-operational designs of the early 1960's to the present wideband commercial design requiring considerable on-site manpower. A critical part of these earth terminals is the broadband, low noise receiver connected between the antenna and the down converter or filter-multiplexer for individual channels. Typically, the low noise receiver takes the form of a cryogenic parametric amplifier employing a two-stage refrigerator to provide temperatures on the order of 20.degree.K. Such amplifiers have extremely low noise figures but somewhat marginal reliability figures.
Due to the growing and changing needs of satellite communication systems, it is clear that automatic earth terminals with a high degree of reliability are required to provide economic and quality service in the future. In the low noise receiver of an earth terminal, failure of a cooled stage or of the refrigerator is catastrophic. This failure can be overcome, however, by switching to a redundant receiver unit. Even so, since both units would have been running continuously since the last maintenance, the probability of survival of one of the two is not greatly enhanced. The net result is at best a complicated and expensive receiver requiring a redundant receiver unit, refrigerators, Dewars, switches, and considerable monitoring equipment.